The invention relates generally to a magnetron for deposition of sputtered material onto a semiconductor substrate.
A semiconductor integrated circuit contains many layers of different materials usually classified according to whether the layer is a semiconductor, a dielectric (electrical insulator) or metal. However, some materials such as barrier materials, for example, TiN, are not so easily classified. The two principal current means of depositing metals and barrier materials are sputtering, also referred to as physical vapor deposition (PVD), and chemical vapor deposition (CVD).
One conventional sputter reactor has a planar target in parallel opposition to the wafer or other semiconductor substrate being sputter deposited. A negative DC voltage is applied to the target sufficient to ionize the argon working gas into a plasma. The positive argon ions are attracted to the negatively charged target with sufficient energy to sputter atoms of the target material. Some of the sputtered atoms strike the wafer and form a sputter coating thereon. Often a magnetron is positioned in back of the target to create a magnetic field adjacent to the target. The magnetic field traps electrons, and, to maintain charge neutrality in the plasma, the ion density increases also. As a result, the plasma density and sputter rate are increased. The conventional magnetron generates a magnetic field principally lying parallel to the target.
Much effort has been expended to allow sputtering to effectively coat metals and barrier materials deep into narrow holes. High-density plasma (HDP) sputtering has been developed in which the argon working gas is excited into a high-density plasma. Typically, an HDP sputter reactor uses an RF power source connected to an inductive coil adjacent to the plasma region to generate the high-density plasma. The high argon ion density causes a significant fraction of sputtered atoms to be ionized. If the pedestal electrode supporting the wafer being sputter coated is negatively electrically biased, the ionized sputter particles are accelerated toward the wafer to form a directional beam that reaches deeply into narrow holes.
Another sputtering technology, referred to as self-ionized plasma (SIP) sputtering, has been developed to fill deep holes. See, for example, U.S. patent application Ser. No. 09/373,097 filed Aug. 12, 1999 by Fu and U.S. patent application filed Oct. 8, 1999 by Chiang et al. In one implementation, SIP uses a capacitively coupled plasma sputter reactor having a planar target in parallel opposition to the wafer being sputter coated. A magnetron positioned in back of the target increases the plasma density and hence the sputtering rate. In some implementations, the target is separated from the wafer by a large distance to effect long-throw sputtering, which enhances collimated sputtering. Asymmetric magnetic pole pieces cause the magnetic field to have a significant vertical component extending far towards the wafer, thus extending the high-density plasma volume and promoting transport of ionized sputter particles.
The SIP technology can be used for sustained self-sputtering (SSS) in which a sufficiently high number of sputter particles are ionized that they may be used to further sputter the target and no argon working gas is required. Of the metals commonly used in semiconductor fabrication, copper is susceptible to SSS resulting from its high self-sputtering yield.
The extremely low pressures and relatively high ionization fractions associated with SSS are advantageous for filling deep holes with copper. However, it was quickly realized that the SIP technology could be advantageously applied to the sputtering of aluminum and other metals and even to copper sputtering at moderate pressures. SIP sputtering produces high quality films exhibiting high hole filling factors regardless of the material being sputtered. Other sputter geometries have been developed which increase the ionization density. One example is a multi-pole hollow cathode target, several variants of which are described by Barnes et al. in U.S. Pat. No. 5,178,739. Its target has a hollow cylindrical shape, usually closed with a circular back wall, and is electrically biased. Typically, a series of magnets, positioned on the sides of the cylindrical cathode of alternating magnetic polarization, create a magnetic field extending generally parallel to the cylindrical sidewall. Helmer et al. in U.S. Pat. No. 5,482,611 discusses a hollow cathode target in which an axially polarized tubular magnet surrounds the sides of the hollow cathode and extend in back of the cathode back wall to create a generally axial magnetic field but which forms a cusp at the cathode back wall. Another approach uses a pair of facing targets facing the lateral sides of the plasma space above the wafer.
A source of sputtered deposition material has, in one embodiment, a torus-shaped plasma generation area in which a plasma operates to sputter the interior surface of a cathode. In one embodiment, the sputtered deposition material may pass to the exterior of the source through apertures which may be provided in the cathode itself. The shapes and positions of the apertures may be selected to provide a particular deposition pattern.
In one embodiment, a torus-shaped magnetic field may be generated in the torus-shaped plasma to facilitate plasma generation, sputtering of the cathode and ionization of the sputtered material by the plasma. The magnetic field may be generated using permanent magnets or electromagnetic coils. The coils of the electromagnet may encircle the cathode or may be positioned coaxially with a central axis of the cathode.
In one embodiment, the cathode may be torus-shaped and a ring-shaped anode may be positioned inside the cathode. Alternatively, the cathode and anode may be formed from surfaces having a partial-torus shape.
In one embodiment, ionized deposition material may be attracted to the source apertures by potentials applied to a grill defining the apertures. The flow of ionized deposition material exiting the source may be deflected into particular trajectories by electric fields provided by a lens structure exterior to the source. The shapes and positions of the lens may be selected to provide a particular deposition pattern.
In one embodiment, both the chamber exterior and the cathode may be biased to a ground potential. A flow of coolant may be directed to the cathode such that the coolant is in thermal and electrical contact with the cathode.
There are additional aspects to the present inventions. It should therefore be understood that the preceding is merely a brief summary of some embodiments and aspects of the present inventions. Additional embodiments and aspects of the present inventions are referenced below. It should further be understood that numerous changes to the disclosed embodiments can be made without departing from the spirit or scope of the inventions. The preceding summary therefore is not meant to limit the scope of the inventions. Rather, the scope of the inventions is to be determined by appended claims and their equivalents.